1. Field of the Invention
This invention relates to a tubular, dimensionally heat recoverable, polymeric article comprising a spirally wrapped polymeric sheet, to methods of making the article, and to methods of using the article to bridge two elongate substrates.
2. Introduction to the Invention
A dimensionally heat recoverable article is an article the dimensional configuration of which may be made substantially to change when subjected to heat treatment. Usually these articles recover towards an original shape from which they have previously been deformed but the term "recoverable", as used herein, also includes an article which adopts a new configuration, even if it has not been previously deformed. In their most common form, heat recoverable articles comprise a shrinkable sleeve made from polymeric material.
Commonly, processes for producing heat recoverable articles involve cross-linking the polymer at some stage in the production process to enhance the desired dimensional recoverability. A particular method of producing a heat recoverable article comprises shaping the article into the desired heat stable form, subsequently cross-linking the polymeric material, heating the article to a temperature above the crystalline melting point or, for amorphous materials the softening point, as the case may be, of the polymer, deforming the article and cooling the article whilst in the deformed state so that the deformed state of the article is retained. In use since the deformed state of the article is heat unstable, application of heat will cause the article to assume its original heat stable shape. Cross-linking may conveniently be carried out by irradiation, or by chemical means.
European Publication No. 0158519 describes a heat recoverable article for covering elongate substrate(s), the article comprising a heat recoverable, cross-linked, polymeric sheet having a resistance heating element arranged in thermal contact with the sheet, the resistance element being connected to a source of electrical power to heat and hence recover the article. In order to install the article, the sheet containing the heating element is spirally wrapped one or more times around the substrate(s) prior to the heating. The sheet is usually lined with adhesive, and after heating and recovery, adjacent layers of the sheet are bonded to each other.
Relatively thin wall tubular products (wall thickness 0.4 to 2 mm), apparently comprising spirally wrapped, cross-linked, polyethylene layers, overlapping layers of which are pre-bonded to each other by copolymer bonding layers, probably an ethylene vinylacetate bonding layer, have been available on the market for a number of years. These thin wall sleeves typically range in diameter from about 50 to 1000 mm, and typically find application for pipe covering and the like.
Japanese Patent Publication No. 54-163974 (Hitachi) describes a method of making a heat shrinkable composite pipe by winding a tape of two or more water cross-linkable polymers around a mandrel, integrating the layers by heat, and subsequently cross-linking the polymers in water or humidity. The pipe is made heat shrinkable by introducing a pressurized fluid to expand it, and cooling in the expanded shape.
Japanese Patent Publication No. 61-249738 (Futukawa) describes a method of making a heat shrinkable polyolefin coating material by winding silane graft polyolefin sheet onto a mandrel, in the presence of a silanol condensation catalyst, to give a laminate of a desired thickness. The wound sheet is then heated to weld the overlapping layers and to cross-link. The cross-linked tube is then expanded and cooled in the expanded shape.